1. Field of the Invention
The invention relates to a short arc lamp which is used for a light source for a projector, semiconductor exposure and ultraviolet curing or for similar purposes.
2. Description of the Related Art
For a light source for a projector, for example, a short arc lamp which is filled with xenon gas is conventionally often used. Recently, however, there has been a great demand for even greater brightness of the projection images of the projector. Therefore, there is the tendency for the amount of added xenon gas to become greater and greater. Short arc lamps, therefore, have recently had an extremely high gas pressure within the arc tube during operation.
In this short arc lamp, a fused silica glass, spherical or oval arc tube is filled with xenon gas, and furthermore, an anode and a cathode are disposed opposite one another. A side tube is connected to the two ends of the arc tube. On the ends of the side tube, upholding parts of the cathode and anode are sealed. To hold the cathode and anode upholding parts securely, the ends of the side tube on the arc tube sides are shrunk by heating so that shrunken areas with a smaller diameter are formed. To directly hold the upholding parts of the cathode and anode together in the shrunken regions of the side tubes it is, however, necessary to draw the side regions very strongly. The upholding parts of the cathode and anode are, therefore, inserted into cylindrical retaining bodies of fused silica glass and the shrunken areas of the side tube are welded to the cylindrical retaining bodies. In this way, the upholding parts of the electrodes of the cathode and anode are held securely.
As was described above, the shrunken regions of the side tube are welded by heat to the cylindrical retaining bodies and formed into a single part. However, if the side tube is heated over the entire area of the cylindrical retaining bodies in the longitudinal direction, and thus, shrunken regions are formed, at the locations of the shrunken regions 12 which lie above and beyond the faces of the cylindrical retaining bodies 30, suspended locations 14 are formed, as shown in FIG. 5.
Between the faces of the cylindrical retaining bodies 30 which are welded to the shrunken regions 12 and which are formed into a single part and the suspended locations 14, therefore, small wedge-shaped gaps 15 are formed.
If, to prevent formation of these suspended locations 14, the side tube 11 is heated only as far as in front of the ends of the cylindrical retaining bodies 30, shrunken regions 12 are formed which are not welded at the ends of the cylindrical retaining bodies 30, as shown in FIG. 6 because the part of the side tube 11 which corresponds to the ends of the cylindrical retaining bodies 30 is not heated. These areas form wedge-shaped gaps 15. This means that, in any case, in the corner areas of the faces of the shrunken regions 12 and the cylindrical retaining bodies 30, small wedge-shaped gaps 15 are formed.
As was described above, small wedge-shaped gaps 15 form in the corner areas of the faces of the shrunken regions 12 and the cylindrical retaining bodies 30, when the shrunken regions 12 and cylindrical retaining bodies 30 are welded and made into a single part. Furthermore, since the gas pressure within the arc tube 10 is extremely high during operation, stress is concentrated in the area these wedge-shaped gaps 15, by which cracks form proceeding from them. By means of repeated application of stress, the cracks grow extensively in the diagonal direction; this can ultimately lead to breakage of the lamp in the corner areas of the faces in which the shrunken regions 12 and the cylindrical retaining bodies 30 are in contact will one another.
Therefore, a primary object of the present invention is to devise a short arc lamp with a high lamp sustaining voltage in which there is no crack formation in the corner areas of the faces of the shrunken regions of a side tube and of the cylindrical retaining bodies for the upholding parts of the electrodes, even if the gas pressure is high during operation.
According to the invention, in a short arc lamp in which, in an arc tube, there are a cathode and an anode disposed opposite one another, in which upholding parts of the cathode and anode are inserted and held in cylindrical retaining bodies, and in which these cylindrical retaining bodies are supported in shrunken regions of a side tube connected to the arc tube, this object is achieved by intermediate layers of metal or ceramic being located between the cylindrical retaining bodies and the shrunken regions, and by the cylindrical retaining bodies and the shrunken regions not being welded to one another, i.e. they are not formed into a single part.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show several embodiments in accordance with the present invention.